پترولوژی و سن سنجی زیرکن به روش U-Pb در توده های نفوذی مناطق A، C جنوبی و دردوی، معدن سنگ آهن سنگان خواف

Abstract

Sangan magnetite skarn mine is located 300 km southeast of Mashhad, along the eastern part of Khaf-Drouneh volcanic-plutonic belt. Granitoids from three areas within the Sangan mine A, C-North and Dardvay were studied. Within the study area, three intrusive rocks including biotite-hornblende monzonite porphyry, biotite syenite and syenogranite were recognized. Based on field cross cutting, absence of garnet-magnetite skarn around the contact, and alteration by younger hydrothermal fluids, these granitoids are older than the magnetite skarn. U-Pb zircon age of the granitoid is 42 Ma (Middle Eocene). Magnetic susceptibility of the granitoids are 310-900 × 10-5 (SI units) and therefore, they are classified as belonging to the magnetite-series (oxidant type) I-type. Chemically, these granitoids are metaluminous, alkali-calcic to alkali and shoshonite to ultrapotassic. Enrichment of LREE, relative to HREE and enrichment of LILE (Sr, Cs, Rb, K and Ba) relative to HFSE (Nb, Ta, Ti, Hf and Zr) indicate that the magma formed in island arc setting. This magma originated from low partial melting (<1%) of garnet-spinel lherzolite (low garnet) and was contaminated in the continental crust. Based on the ratio of (La/Yb)N 6.23-34.73, indicate that small amount of garnet was left in the source rock. High ration of Rb/Sr, LILE/HFSE and high content of K2O, Th and Nb indicative of continental crust contamination. Petrognesis and geochronology of Sangan granitoid will help to know more about tectonomagmatic of Khaf-Kashmar-Drouneh volcanic-plutonic belt and their mineralization.